In a closed loop hydraulic or hydrostatic circuit, flow is exhausted from the working circuit for the purposes of cooling and filtering. If this is the only system contributing to a particular work function (a hydrostatic drive, for example), exhausting this oil only during powered operation is generally acceptable. If the system is assisted or provides assistance to another system (a part time hydrostatic drive on a machine that is primarily driven by a traditional transmission, for example) a means of exhausting oil in a non-powered (standby) condition may be necessary.
Previous efforts include splitting the traditional hydrostatic flushing system between two separate devices. For example, a motor grader vehicle can include a hydrostatic loop flushing system that is independent from the drive motor case flushing system. Typical hydrostatic loop flushing exhausts flow from the low pressure side of the work circuit prior to sending it to the hydraulic oil cooler and reservoir. A separate system utilizes a small pump to send constant flow to the cases of the drive motors. This provides benefits similar to an open center loop flushing system, but does so by utilizing extra components and hydraulic circuits which add costs and complexity.
It would be desirable to have a hydrostatic loop flushing system that always flushes fluid through the system whether the hydrostatic circuit is in a powered or unpowered state.